The Foals fell to their third defeat of the season to remain in 12th position in the Bundesliga with a comprehensive defeat at the Weser Stadion and the Swiss coach is growing tired with his side's defensive errors.
"I have said it over and over again, and still have to keep repeating myself - we have a lot of work to do and I regret that we are conceding unnecessary goals," he said.
"Above all, the 2-0 was unnecessary, and also the 3-0 - we are losing the ball in midfield and it is incredible.
"We have to carry on working and discussing things, but we need to play with more belief.
"We forget to defend at times and we are paying dearly."
Bremen coach Thomas Schaaf preferred to see the merits in his side's attack rather than a poor defensive performance from Gladbach, saying: "We did not just react, but we constantly attacked our opponents.
"We tried to decide things in our favour," he added on Sky television.
The win lifted Bremen above their opponents into ninth position, just a point behind the top six and a place in Europe next season - the aim both teams had at the start of the campaign.